c++11 std::array init

[Chris Forone]

hello group,

why can i initialize a local std::array in this way:

std::array<float, 3> locvar{1.0f, 2.0f, 3.0f};

but as member "only" in this way:

std::array<float, 3> member{{1.0f, 2.0f, 3.0f}};

i use mingw g++ 4.8.0 (32 bit).

thanks a lot, chris

[Sam]

Chris Forone writes:

> hello group,
>
> why can i initialize a local std::array in this way:
>
> std::array<float, 3> locvar{1.0f, 2.0f, 3.0f};

Because you can't. That's the short answer.

> but as member "only" in this way:
>
> std::array<float, 3> member{{1.0f, 2.0f, 3.0f}};

These are two different things. The first one would be a constructor with
variadic parameters. The second one is a std::initializer_list. It shouldn't
be surpising that something called a "std::initializer_list" would be used
to initialize something.

I suppose that there is no technical reason why a variadic list of
parameters cannot be used to initialize an array or a vector, but that's
just the way it is.

[Chris Forone]

Am 16.05.2013 12:49, schrieb Sam:
> Chris Forone writes:
>
>> hello group,
>>
>> why can i initialize a local std::array in this way:
>>
>> std::array<float, 3> locvar{1.0f, 2.0f, 3.0f};
>
> Because you can't. That's the short answer.
>

but i do and it compiles fine!

>> but as member "only" in this way:
>>
>> std::array<float, 3> member{{1.0f, 2.0f, 3.0f}};
>
> These are two different things. The first one would be a constructor
> with variadic parameters. The second one is a std::initializer_list. It
> shouldn't be surpising that something called a "std::initializer_list"
> would be used to initialize something.
>
> I suppose that there is no technical reason why a variadic list of
> parameters cannot be used to initialize an array or a vector, but that's
> just the way it is.
>

can a ctor have both kinds of braces? () {}
im not surprised about the function of the initializer_list and dont
understand it, if there is some kind of (sarcastic?) joke in there...

[Chris Forone]

Am 16.05.2013 12:49, schrieb Sam:

ok, i think i understand now: the one is brace elision with copy-ctor,
the other is direct aggregate-initialization of the c-style array in
std::array<>

cheers, chris